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Fire is rapid, self-sustaining oxidation accompanied by the evolution of varying intensities of heat and light. This definition indicates that fire is a chemical process of decomposition in which the rapid oxidation of a fuel produces heat and light.
Fire Triangle
Three basic elements must be present for a fire to occur: fuel, heat, and oxygen. These three components make up the fire triangle , and proper combination of these three items invariably results in a fire. There must be oxygen to sustain the combustion, heat to raise the material to its ignition temperature, Fuel to support the combustion and a Chemical reaction between the three elements. The chemical chain reaction between the fuel, heat, and oxygen represents the fourth component of the fire equation. We will refer to this as the fire tetrahedron. Anytime something burns, these four components are present. Preventing the combination of these elements will prevent a fire. If one of the four elements is removed from the fire situation, the fire will be extinguished.
In a fire, it is the vapors that are actually burning, so the closer the fuel is to the vapor state, the easier it is to ignite. Liquids ignite more readily than solids, gases more easily than liquids.
The physical state of the fuel is also important. A solid wooden board is more difficult to ignite than wood shavings due to the mass to surface area ratio. If the mass is large and the surface area small, as with the solid board, the heat of an ignition source is more easily dissipated through the material and hence there is less chance for ignition and fire. If the mass is small and the surface area large, as with wood shavings, the heat cannot be dissipated as quickly, and ignition occurs more easily.
Dust is an example of reducing mass relative to the surface area. Given the proper conditions, many dusts may explode. Grain and coal dust are two common varieties of dust that can explode
Classification of Fire
Class A fires involve ordinary combustible materials: wood, paper, trash, plasic and cloth. Class A fires are usually relatively slow in their initial development and growth, and because these materials are solids, they are somewhat easier to contain. Class A fires leave an ash after the material has been consumed.
Class A Fire
Class B fires involve flammable and combustible liquids and flammable gases such as Gasoline, Fuel oil, Paint, Butane and Propane. These fires usually develop and grow very rapidly. Class B materials are fluid in nature, which allows them to flow and move. This makes dealing with them somewhat more difficult than Class A materials. These materials are common in many settings. These fires typically do not leave an ash.
Class B Fire
Class C fires involve energized electrical equipment such as motors, appliances, and machinery. This is the only classification of the five that is not directly related to the type of fuel. The fact that a live electrical circuit is involved is the determining factor. Remove the power and the burning materials may actually fall into one or more of the four other classes. If the electric power is disconnected, the fire is no longer considered class C. Whether the device being considered is turned on or not is unimportant in this classification. Power to the device makes it Class C even if the device is turned off.
Class C Fire
Class D fires involve combustible metals such as Potassium, Sodium, Magnesium, Aluminium, Titanium, and Zirconium. These materials are usually difficult to ignite but create intense fires once started. Class D fires are very difficult to extinguish, but, fortunately, they are relatively uncommon in most industries.
Class D Fire
Class K fires involve cooking oils and greases such as animal fats and vegetable fats. This is the newest of the fire classes.
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